The present invention is related to systems for detecting target ions in a sample and methods of use thereof in clinical laboratory instrumentation.
Throughout this application, various references are referred to within parentheses. The disclosures of these publications in their entireties are hereby incorporated by reference into this application to more fully describe the state of the art to which this invention pertains. Full bibliographic citation for these references may be found at the end of this application, preceding the claims.
An important sensing platform in ion analyses is the bulk optode, which contains a selective and lipophilic ionophore, a chromoionophore and an ion-exchanger entrapped within a polymeric film coated onto a suitable support. Chromoionophores are normally lipophilic pH indicators used in ion selective optodes. Such dyes usually require sufficient lipophilicity (log PTLC>10.6), a large molar extinction coefficient, a high chemical and photostability and a high selectivity to H+ (1, 2). Chromoionophores may be classified into neutral and charged chromoionophores, depending on the electrical charge of their unprotonated form. In the past two decades, a series of lipophilic H+ selective chromoionophores of different basicities were synthesized (2). The lipophilic H+ selective chromoionophores may be combined with different ionophores to design optodes with different measuring ranges for specific analytical needs (2).
Many of these chromoionophores are highly lipophilic and suitable for general applications. However, optodes based on these chromoionophores exhibit short lifetime in lipophilic samples such as undiluted serum. Further, the leaching of plasticizer and other sensor components is more dramatic when the size of the sensor is reduced to microparticles in the micro-meter range (3) or nanometer range (4, 5). Further, to prevent an inflammable response in in-vivo measurements with such sensors and to avoid cross-contamination between adjacent microspheres, the sensing components including chromoionophores are immobilized onto the polymer matrix.
In earlier work, chromoionophores have been covalently attached onto functionalized poly(vinyl chloride) (6, 7) and onto polyurethane matrices (8), but such polymers could not be used without plasticizer and lead to longer response time. On the other hand, immobilization of non-chromogenic ionophores onto polymers has been more widely studied. Ionophores selective for Na+, K+ and Pb2+ have been covalently grafted to a polysiloxane matrix and applied to the fabrication of CHEMFET sensors (9, 10).
Kimura introduced a sol-gel technique to immobilize ionophores and ion exchangers (11, 12, 13). Another direction in ionophore grafting is to copolymerize the polymerizable ionophores with blank polymers by a one-step solution polymerization method. This type of procedure was utilized for the covalent attachment of two hydrophilic crown ether-type potassium-selective ionophores, 4′-acryloylamidobenzo-15-crown-5 (AAB15C5) and 4′-acryloylamidobenzo-18-crown-6 (AAB18C6) (14, 15, 16), a sodium-selective ionophore, 4-tertbutyl calix[4]arene tetraacetic acid tetraethyl ester (17), a calcium ionophore, N,N-dicyclohexyl-N′-phenyl-N′-3-(2-propenoyl)oxyphenyl-3-oxapentanediamide (AU-1) (16) as well as polymerizable anion ion-exchangers (18) onto an acrylic polymer. The simplicity of this procedure constitutes an important advantage over most other methods described above. These polymers containing grafted ionophores showed comparable selectivity and improved lifetime compared to ISEs based on free, unbound ionophore.
There is a need for improved chromoionophores remedying the defects of the prior art.